Ledger autopsy results to take 10 days

New York's chief medical examiner will need at least a further 10 days to determine the cause of Heath Ledger's death, after an autopsy overnight failed to deliver conclusive results.

The 28-year-old actor was found lifeless in his Manhattan apartment yesterday morning, with a number of prescription pills near his naked body. (Photos from the scene)

The 90-minute autopsy was "inconclusive", according to a medical spokeswoman, and it will take days for blood and tissue samples taken from Ledger to show up traces of legal or illegal drugs.

"If anything is found they go back and identify and quantify whatever they have," the spokeswoman said.

Although official accounts have so far only mentioned the presence of prescription medicines, there are reports a $20 bill discovered at the scene had traces of a "narcotic residue".

Another report by American TV network CBS suggested there were "several drug packets containing an unknown substance", quoting sources close to the investigation.

Bottles of the generic forms of Xanax and Valium, both anti-anxiety drugs prescribed in his name, were found at his $26,000-a-month, three-bedroom loft apartment. (Map: Ledger's Soho address)

Police also found sleeping pills Donormyl, Zopiclone, and Ambien, the New York Post reported, quoting a police source who said: "it does not appear to be a suicide". (Ledger's sleeping pill 'controversial')

Veteran actor Jack Nicholson said he had warned Ledger about the dangers of sleeping pills, describing a life-threatening experience he had had with Ambien, known as "Stilnox" in Australia.

"I took Ambien once," Nicholson said.

"I fell asleep and then got a call and almost drove off a cliff 50 yards from my house."

Ledger was found lying face down and unresponsive by his maid, Theresa Solomon, and masseuse Diane Lee at 3.20pm local time (7.20am AEDT) .

Ms Solomon said she had heard the actor snoring at midday.

The maid and therapist called 911 at 3.26pm. Emergency workers were unable to revive the star and he was pronounced dead at 3.35pm.

"We are investigating the possibility of an overdose," NYPD spokesman Paul Browne said.

"There were pills within the vicinity of the bed."

According to friend Sophie Ward, Ledger was anxious about the breakdown of his relationship with the mother of his child while he was home in Perth for Christmas.

"He was clean and wasn't drinking any alcohol or taking drugs," Ms Ward, sister of supermodel Gemma who had been linked to Ledger, said.

"We went to the movies and just did normal stuff ... but he was a bit edgy. He couldn't really relax."